1. Field of the Invention.
This invention pertains to force activated releasable restraint devices and more particularly to such devices which restrain aircraft prior to catapult assisted takeoffs.
2. Description of the Prior Art
Modern highspeed aircraft operating from aircraft carrier decks require assistance in reaching their minimum flying speed when attempting to take off. This assistance may take the form of a steam powered catapult or the like. In such catapult assisted launches the aircraft must be restrained while pressure in the catapult is built up and jet engines reach full power. Also, powerful jet engines in takeoff power condition may create thrust which exceeds the capacity of the wheel brakes. When catapult pressure is up, and engine power full, the restraint device must release quickly and cleanly.
Prior devices have used expendible tensile links which part at a predetermined force level. These devices are limited in that a new link is required for each launch, expended links clutter the deck and create a foreign object hazard to personnel and deck machinery, and can be ingested by jet engines. The tensile links are expensive to manufacture and store, and are worthless after one use. Also, each different type aircraft requires a different strength tensile link.
One reusable restraint device is described in U.S. Pat. No. 3,578,273, issued May 11, 1971 to Thomas Mulgrave. This device uses a spring biased ball valve to trigger release of gripping fingers from structure attached to an aircraft. Hydraulic pressure caused by application of launching forces eventually unseats the spring biased ball, and hydraulic fluid escapes to permit movement of a piston relative to a housing. This movement in turn causes release of the gripping fingers from structure attached to the aircraft. This device is different from the present invention as will be explained in a description which follows.
The Mulgrave device has the advantage of being reusable, but in order to change the force level at which release occurs, the ball valve bias spring must be either replaced with a different strength spring, or the preload on the spring must be changed. This is necessary to accomodate aircraft of different masses which require different launching forces to achieve adequate acceleration to reach minimum flying speed from limited deck lengths.